U.S. patent number 3,895,611 [Application Number 05/406,109] was granted by the patent office on 1975-07-22 for air-fuel ratio feedback type fuel injection system.
This patent grant is currently assigned to Nippondenso Co., Ltd.. Invention is credited to Kunio Endo, Susumu Harada, Junji Kawarada, Hideaki Norimatsu, Motoharu Sueishi.
United States Patent |
3,895,611 |
Endo , et al. |
July 22, 1975 |
Air-fuel ratio feedback type fuel injection system
Abstract
There is provided an air-fuel ratio feedback type fuel injection
system of the type in which the fuel quantity is controlled to suit
various operating conditions of an engine by a computing unit for
generating injection pulses which determine the duration of the
opening of electromagnetic valves connected to a fuel line in which
the pressure is maintained at a constant value. The system further
comprises an oxygen concentration detector for detecting the
concentration of oxygen contained in the exhaust gases, an air-fuel
ratio discriminating circuit for comparing the detected signal from
the oxygen concentration detector with a preset value to make a
discrimination, a samplying signal generating circuit for
generating a samplying signal having a predetermined frequency to
sample the discrimination signals from the air-fuel ratio
discriminating circuit, and a feedback system for providing
negative feedback to the computing unit to reverse the
discrimination signal.
Inventors: |
Endo; Kunio (Anjo,
JA), Kawarada; Junji (Kariya, JA), Sueishi;
Motoharu (Kariya, JA), Harada; Susumu (Oobu,
JA), Norimatsu; Hideaki (Kariya, JA) |
Assignee: |
Nippondenso Co., Ltd. (Kariya,
JA)
|
Family
ID: |
27552170 |
Appl.
No.: |
05/406,109 |
Filed: |
October 12, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Oct 17, 1972 [JA] |
|
|
47-103727 |
Oct 19, 1972 [JA] |
|
|
47-104799 |
Oct 28, 1972 [JA] |
|
|
47-108220 |
Nov 6, 1972 [JA] |
|
|
47-110930 |
Nov 7, 1972 [JA] |
|
|
47-111750 |
Nov 9, 1972 [JA] |
|
|
47-112440 |
|
Current U.S.
Class: |
123/694; 60/276;
968/817 |
Current CPC
Class: |
F02D
41/1482 (20130101); G04F 5/00 (20130101); F02M
51/02 (20130101); F02D 41/28 (20130101); F02D
41/1456 (20130101) |
Current International
Class: |
F02M
51/02 (20060101); F02D 41/00 (20060101); F02D
41/24 (20060101); F02D 41/14 (20060101); G04F
5/00 (20060101); F02b 003/00 () |
Field of
Search: |
;123/32EA
;235/150.21 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Antonakas; Manuel A.
Assistant Examiner: Cranson, Jr.; James W.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
We claim:
1. An air-fuel ratio feedback type fuel injection system having
electromagnetic valve means connected to a constant pressure fuel
line to inject the fuel into an internal combustion engine mounting
the fuel injection system and a computing unit connected through an
electromagnetic valve actuating circuit to the electromagnetic
valve means for generating an injection pulse signal to determine
the opening duration of the electromagnetic valve means thereby to
control the quantity of said fuel to suitable various operating
conditions of the internal combustion engine, comprising:
an oxygen concentration detector mounted in an exhaust pipe of said
engine for detecting the concentration of oxygen contained in the
exhaust gases of said engine,
an air-fuel ratio discriminating circuit means connected to said
oxygen concentration detector for comparing an output signal of
said detector with a predetermined value to generate an output
signal,
a sampling signal generating circuit means for generating a
sampling signal having a predetermined frequency,
an addition and subtraction command circuit means connected to said
sampling signal generating circuit means and said air-fuel ratio
discriminating circuit means for generating an output command
signal in accordance with the output signal of said air-fuel ratio
discriminating circuit each time said sampling signal is applied
thereto,
a reversible counter connected to said addition and subtraction
command circuit means to perform the operation of addition or
subtraction on the count thereof in accordance with said output
command signal of said addition and subtraction command circuit
means for generating a correction signal, and
valve opening duration correcting means connected to said
reversible counter and further to said computer unit for
controlling the opening duration of said electromagnetic valve
means in accordance with said correction signal of said reversible
counter in cooperation with said computing unit to reverse the
output signal of said air-fuel ratio discrimination circuit means
by changing the quantity of said fuel through said valve means.
2. A fuel injection system according to claim 1, wherein said valve
opening duration correction means comprises a D-A converter.
3. A fuel injection system according to claim 1, wherein said valve
opening duration correcting means comprises a correction value
setting circuit means connected to said reversible counter and to
said computing unit for generating a correction pulse signal
corresponding to the correction signal of said reversible counter
to extend the duration of the opening of said electromagnetic valve
means.
4. A fuel injection system according to claim 1 further comprising
a power range detector means connected to said valve opening
duration correcting means for detecting a power range requiring a
large torque in said engine and stopping the operation of said
valve opening duration correcting means when said power range is
detected.
5. A fuel injection system according to claim 1 further comprising
a holding circuit means connected to said reversible counter for
maintaining the count of said reversible counter at the maximum or
minimum value thereof when the count of said reversible counter
exceeds the maximum or minimum capacity of said reversible
counter.
6. A fuel injection system according to claim 1 further comprising
means connected to said sampling signal generating means for
varying the frequency of the sampling signals from said sampling
signal generating means in accordance with the response time of
said oxygen concentration detector.
7. A fuel injection system according to claim 1 further comprising
superposing means connected to said sampling signal generating
circuit, to said valve opening duration correcting means and to
said computing unit for superposing an additional correction signal
corresponding to the number of the sampling of said sampling
signals effected in a time interval up to the reversal of the
output signal of said air-fuel ratio discriminating circuit means
on the output signal of said valve opening duration correcting
means.
8. A fuel injection system according to claim 1 further comprising
dead zone detecting means connected to said oxygen concentration
detector and to said sampling signal generating circuit means for
preventing the generation of the output signal of said addition and
subtraction command circuit when the output of said oxygen
concentration detector reaches the level of an intermediate
zone.
9. A fuel injection system according to claim 1, wherein said
sampling signal generating circuit means generates said sampling
signals in synchronism with the rotation of said engine.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fuel injection systems and more
particularly to an electric fuel injection system which
incorporates an air-fuel ratio feedback control.
2. Description of the Prior Art
Fuel injection systems are known in the art in which the quantity
of fuel fed to the engine is controlled by measuring the quantity
of air drawn into the engine and programming the fuel quantity
predetermined in accordance with the quantity of air in terms of
the duration of the energization of electromagnetic valves. A
disadvantage of this type of fuel injection system is that even if
various engine parameters such as the manifold vacuum and engine
temperature are detected to control the fuel quantity, it is
extremely difficult to compensate for the ever changing operating
conditions of the engine, the variations by different engines and
so on so as to always operate the engine with a predetermined
air-fuel ratio. The difficulty especially gives rise to a serious
problem with an engine equipped for example with a catalytic
purifier for purifying the exhaust gases.
SUMMARY OF THE INVENTION
With a view to overcoming the foregoing difficulty, it is an object
of the present invention to provide an air-fuel ratio feedback type
fuel injection system wherein the concentration of oxygen contained
in the exhaust gases is detected so that the duration of the
energization of the electromagnetic valves is corrected in
accordance with the detected output to operate the engine with a
predetermined air-fuel ratio.
It is another object of the present invention to provide such
air-fuel ratio feedback type fuel injection system wherein a signal
representing the detected oxygen concentration is compared with a
reference value for discrimination and the resultant discrimination
signal is sampled to cause a reversible counter to perform the
operation of addition or subtraction in accordance with the sampled
signal and wherein there are included a feedback system for
negatively feeding back the count of the reversible counter to a
computing unit of the fuel injection system which generates
injection pulses for controlling the fuel quantity and a holding
circuit whereby the count of the reversible counter greater than
its maximum counting capacity is held at the allowable maximum or
minimum value, thereby always operating the engine with a
predetermined air-fuel ratio and further minimizing possible
negative feedback errors due to the limitation by the maximum
counting capacity of the reversible counter.
It is still another object of the present invention to provide such
air-fuel ratio feedback type fuel injection system wherein when the
response speed of the oxygen concentration detector decreases, the
frequency of sampling signals for the negative feedback control is
decreased to correct the duration of the energization of the
electromagnetic valves to ensure a predetermined air-fuel ratio
with an improved accuracy.
It is still another object of the present invention to provide such
air-fuel ratio feedback type fuel injection system comprising
superposing means for superposing an additional correction signal
corresponding to the number of sampling by the sampling signals
effected in the time interval up to the reversal of the polarity of
the feedback, whereby when a correction value is used which is
varied by a predetermined amount for each sampling by the sampling
signal or varied according to the load, the correction value is
increased as a means of eliminating such inconvenience that the
occurrence of a large discrepancy between the reference
characteristic and the desired air-fuel ratio characteristic
results in a large time delay in attaining a predetermined air-fuel
ratio or a stable point for the correction value, whereas such
inconvenience which may be caused by the limitation to the response
speed of the oxygen concentration detector when the frequency of
the sampling signal is increased is also prevented.
It is still another object of the present invention to provide such
air-fuel ratio feedback type fuel injection system wherein dead
zone detecting means is provided to detect the fact that the output
of the oxygen concentration detector has reached the intermediate
dead zone between the "D" level and the "1" level and disable the
sampling operation, whereby the engine is operated with a
predetermined air-fuel ratio and moreover the sampling operation is
stopped when the air-fuel ratio comes to the intermediate dead zone
about the predetermined value thereof to thereby prevent the
occurrence of undesired forward and backward swing of the air-fuel
ratio that may be caused when the engine is operated under a
constant load.
The fuel injection system according to the present invention has a
remarkable advantage in that since it incorporates a feedback
control whereby the concentration of oxygen contained in the
exhaust gases is detected by an oxygen concentration detector to
cause an air-fuel ratio discriminating circuit to determine whether
the air-fuel ratio is richer or leaner than a predetermined value
and the count of a reversible counter is increased or decreased to
obtain a predetermined air-fuel ratio until the air-fuel ratio
discriminating circuit makes a different decision, the air-fuel
ratio can be controlled with much greater accuracy as compared with
conventional electronically controlled fuel injection systems.
Another remarkable advantage of the system of this invention is the
use of a D-A converter which produces the necessary correction
value in the form of a voltage so that when the present invention
is incorporated in a known type of electronically controlled fuel
injection system, the correction value can be easily controlled by
using it as one of the parameters of an internal combustion
engine.
A further remarkable advantage is the fact that since the
correction is effected by changing upward and downward the air-fuel
ratio characteristic of the electronically controlled fuel
injection system installed in an internal combustion engine, such
difficulty as heretofore encountered during the starting period can
be eliminated and the capacity of the required reversible counter
can also be reduced comparatively.
A still further remarkable advantage of the system of this
invention is the use of a power range detector for detecting the
power range of a load range which requires a large output torque to
open and close the feedback system, whereby the air-fuel ratio is
normally maintained at a constant value, whereas in the load range
requiring a large output torque the air-fuel ratio is not
maintained at a constant value to provide a satisfactory output
torque.
A still further remarkable advantage is the use of a holding
circuit whereby when the count of the reversible counter exceeds
its maximum counting capacity, the count is held at the allowable
maximum or minimum value to thereby minimize the occurrence of
errors due to the limits to the maximum counting capacity of the
reversible counter.
BRIEF DESCRIPTION OF THE DRAWING
These and other objects, features and advantages of the present
invention will be apparent from the following detailed description
taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a block diagram showing a first embodiment of an air-fuel
ratio feedback type fuel injection system.
FIG. 2 is an input-output characteristic diagram of the air-fuel
ratio discriminating circuit used in the embodiment of FIG. 1.
FIG. 3 is an input-output characteristic diagram of the D-A
converter used in the embodiment of FIG. 1.
FIG. 4 is an air-fuel ratio characteristic diagram useful for
explaining the operation of the embodiment shown in FIG. 1.
FIG. 5 is a block diagram showing a second embodiment of the fuel
injection system of this invention.
FIG. 6 is an electric wiring diagram shwoing one form of the
principal part of the embodiment shown in FIG. 5.
FIG. 7 is an air-fuel ratio characteristic diagram usefuel for
explaining the operation of the embodiment shown in FIG. 5.
FIG. 8 is an electric wiring diagram showing a third embodiment of
the air-fuel ratio feedback type fuel injection system according to
the invention.
FIG. 9 is an electric wiring diagram showing a fourth embodiment of
the fuel injection system according to the present invention.
FIG. 10 is a time versus output characteristic diagram of the
oxygen concentration detector used in the embodiment shown in FIG.
9.
FIG. 11 and 12 are electric wiring diagrams showing respectively a
first and second embodiments of the sampling signal generating
circuit used in the embodiment shown in FIG. 9.
FIG. 13 is a block diagram showing a fifth embodiment of the fuel
injection system according to the present invention.
FIG. 14 is an electric wiring diagram showing one form of the
principal part of the embodiment shown in FIG. 13.
FIG. 15 is a block diagram showing a sixth embodiment of the fuel
injection system according to the present invention.
FIG. 16 is an electric wiring diagram showing one form of the
principal part of the embodiment shown in FIG. 15.
FIG. 17 is an input-output characteristic diagram of the correction
value setting circuit used in the embodiment shown in FIG. 15.
FIG. 18 is an air content in the exhaust gases versus reference
air-fuel ratio characteristic diagram for the embodiment shown in
FIG. 15.
FIG. 19 is a block diagram showing a seventh embodiment of the fuel
injection system according to the present invention.
FIG. 20 is an air-fuel ratio versus output characteristic diagram
for the oxygen concentration detector and the air-fuel ratio
discriminating circuit used in the embodiment of FIG. 18.
FIG. 21 is an electric wiring diagram showing one form of the
principal part of the embodiment shown in FIG. 18.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in grater detail with
reference to the illustrated embodiments.
Referring first to FIG. 1 showing a first embodiment of the
air-fuel ratio feedback type fuel injection system according to the
present invention, numeral 1 designates an oxygen concentration
detector which comprises a metal oxide such as zirconium dioxide or
titanium dioxide and whose output voltage varies in accordance with
the concentration of oxygen contained in the exhaust gases from an
internal combustion engine. Numeral 2 designates an air-fuel ratio
discriminating circuit for comparing the output of the oxygen
concentration detector 1 with an air-fuel ratio setting voltage VR
to generate a discrimination output signal which is either a "0" or
"1" signal as shown in FIG. 2 depending on whether the detected
oxygen concentration of the exhaust gases is greater than or less
than a preset oxygen concentration or preset air-fuel ratio.
Numeral 3 designates an addition and subtraction command circuit
whereby each time a sampling signal arrives, a command signal which
is either "1" level or "0" level is generated to direct the
operation of addition or subtraction in accordance with the
discrimination signal. Numeral 4 designates a sampling signal
generating circuit for generating sampling signals having a preset
frequency or synchronized with the revolution of the engine and
supplying them to the addition and subtraction command circuit 3.
Numeral 5 designates a reversible counter adapted for operation in
response to the command signal from the addition and subtraction
command circuit 3 to generate at its output a binary signal
representing its count. The reversible counter 5 is designed so
that when the count of the reversible counter 5 exceeds its maximum
counting capacity, the count is held at the maximum value if the
addition is being performed, whereas the count is held at "0" if
the subtraction is being performed. The output of the reversible
counter 5 which is represented by a binary code is applied to a D-A
converter 6 representing a binary code of 2.sup.n .about. 2.sup.o
to generate a stairstep voltage as shown in FIG. 3. This output
voltage is applied to a computing unit 7 of the kind used in a
known type of electronically controlled fuel injection system for
internal combustion engines and it is used as one of the
conventional correction terms or engine parameters to control the
pulse width of the injection pulses. Numeral 8 designates an
electromagnetic valve actuating circuit for amplifying the
injection pulse signals. Numeral 9 designates an electromagnetic
valve which is connected to a constant pressure fuel line and whose
duration of the opening is controlled by the injection pulses.
Numeral 100 designates an engine, 110 an exhaust pipe.
With the construction described above, the operation of the first
embodiment will be described. Let it be assumed that in FIG. 4
illustrating an air quantity versus injection time characteristic
(hereinafter referred to as an air-fuel ratio characteristic) of
the electronically controlled fuel injection system installed in
the engine, a curve b shows the actual air-fuel ratio
characteristic and a curve a represents a preset air-fuel ratio
characteristic to be attained. The oxygen concentration detector 1
and the air-fuel ratio discriminating circuit 2 determine whether
the actual air-fuel ratio is greater than or less than the preset
air-fuel ratio and the reversible counter 5 performs the addition
or subtraction in accordance with the predetermined sampling
signals. The count of the reversible counter 5 is then applied to
the D-A converter 6 to produce a corresponding output voltage and
the computing unit 7 calculates a pulse width corresponding to the
output voltage of the D-A converter 6 to thereby effect an additive
or subtractive correction of the pulse width of the injection
pulses to stabilize it at the proper air-fuel ratio. This stable
point is such that the correction value is stabilized for example
in a range which is approximately corresponding to the count value
nx of the reversible counter 5 (e.g., nx + 1). However, the amount
of change with respect to the air-fuel ratio of unit voltage
.DELTA.v shown in FIG. 3 may be reduced or the capacity of the
reversible counter 5 may be increased so that the correction value
is stabilized with the tolerance corresponding to .+-. 1 count, and
this is settable without giving rise to any practical
inconvenience. Further, depending on the operation of the computing
unit 7 which converts the unit voltage .DELTA.v to a unit
correction value .DELTA..tau., it is possible to preset so that
.DELTA.v = .DELTA..tau., or alternatively the correction value may
be varied according to the engine load if it appears to be more
advantageous in consideration of the amount of change of the unit
voltage .DELTA.v. Assuming now that the operating condition of the
engine is at a point P.sub.1 in FIG. 4, the oxygen concentration
detector 1 and the air-fuel ratio discriminating circuit 2
determine that the mixture is too rich and thus generate a
discrimination signal. As a result, sampling signals are applied to
the reversible counter 5 storing the then current condition and the
count is successively deduced. In other words, the count is deduced
as many times as there are the applied sampling signals until the
output or the discrimination signal of the air-fuel ratio
discriminating circuit 2 is eventually reversed, that is the count
is successively deduced for example by .DELTA.v, 2.sup.. .DELTA.v,
3.sup.. .DELTA.v, . . . , n.sup.. .DELTA.v until a predetermined
air-fuel ratio is attained.
On the other hand, when the operating condition of the engine moves
to a point P.sub.2 shown in FIG. 4, the oxygen concentration
detector 1 and the air-fuel ratio discriminating circuit 2
determine that the air-fuel ratio is less than the desired air-fuel
ratio, that is, the mixture is too lean and a corresponding
discrimination signal is generated. Consequently, the reversible
counter 5 storing the then current condition increases its count as
many times as there are the sampling signals applied thereto until
the output or the discrimination signal of the air-fuel ratio
discriminating circuit 2 is reversed, that is, the reversible
counter 5 repeats its operation so that its count is successively
increased as by .DELTA.v, 2.sup.. .DELTA.v, 3.sup.. .DELTA.v, . . .
, n.sup.. .DELTA.v until a predetermined air-fuel ratio is
attained. Further, the pulse width of the injection pulse signals
is corrected upon each injection by a value corresponding to the
then current nx.sup.. .DELTA.v to provide the proper injection
pulse signals.
Repetition of the above-described process enables the engine to
operate with a predetermined air-fuel ratio over the entire
operating range thereof.
FIG. 5 shows a second embodiment of the present invention which
differs from the first embodiment of FIG. 1 in that a power range
detector comprising a manifold pressure detector 10 and a pressure
level discriminating circuit 11 as shown in FIG. 6 is added to
detect the power range or the load range as in the first embodiment
of FIG. 1. In this power range, therefore, the negative feedback
for maintaining the air-fuel ratio of for example 14.8 is
interrupted to achieve a considerable increase in the output torque
of the engine. In other words, the pressure level discriminating
circuit 11 determines whether the output of the manifold pressure
detector 10 is higher than a preset pressure so that the D-A
converter 6 and the computing unit 7 are switched on or off in
accordance with the output signal of the pressure level
discriminating circuit 11. When the D-A converter 6 and the
computing unit 7 are switched off, the negative feedback is
interrupted. Consequently, as shown in the air-fuel ratio
characteristic diagram of FIG. 7, the engine is operated along the
characteristic curve a up to point P.sub.3, whereas after the point
P.sub.3 the negative feedback is interrupted and the engine is
operated along the characteristic curve b with an air-fuel ratio of
for example 1.3 to 1.35. In this case, the manifold pressure
detector 10 is of the type which is necessarily provided in any
known type of electronically controlled fuel injection system and
therefore it needs not be additionally provided and the
conventional pressure indicator may concurrently be used as the
manifold pressure detector 10 of this invention. Further, since the
detection of the power range, i.e., the comparison of the manifold
pressure with the preset pressure by the pressure level
discriminating circuit 11 requires as a matter of fact the
detection of the differential pressure between the manifold
pressure and the atmospheric pressure, good results may also be
obtained, if a pressure switch which is turned on or off when the
differential pressure between the manifold pressure and the
atmospheric pressure is higher than a predetermined pressure is
used and the signals of the D-A converter 6 and the computing unit
7 are switched on or off in accordance with the output of the
pressure switch to switch on and off the negative feedback.
Further, the position of a baffle plate placed within the intake
manifold to detect the amount of air flow may also be detected to
thereby similarly effect the required on-off control of the
negative feedback.
The circuit construction and operation of a third embodiment of the
air-fuel ratio feedback type fuel injection system according to the
present invention will be described in detail with reference to the
detailed circuit diagram shown in FIG. 8. The third embodiment
differs from the first embodiment of FIG. 1 in that it further
comprises a holding circuit 12. In FIG. 8, numeral 2a designates a
buffer amplifier whereby the output voltage of the oxygen
concentration detector 1 is amplified according to the value of
ratio R.sub.2c /R.sub.2b between resistance values R.sub.2b and
R.sub.2c of an input resistor 2b and a feedback resistor 2c and
delivered to a comparator 2d. In the comparator 2d, the output of
the amplifier 2a is compared with the reference voltage VR obtained
by dividing the potential determined by a Zener diode 2h with
resistors 2e and 2f, so that a "1" signal is generated when the
output of the amplifier 2a is higher than the reference voltage,
whereas a "0" signal is generated when the former is lower than the
latter. In other words, it is arranged so that the output of the
comparator 2d is a "0" signal when the air-fuel ratio is greater
than a predetermined value, whereas the comparator 2d generates a
"1" signal when the air-fuel ratio is lower than the predetermined
value. Further, the comparator 2d is provided with a resistor 2g
which provides a suitable hysteresis to prevent any misoperation of
the output of the comparator 2d (at a speed higher than the
response speed) which may be caused by for example the presence of
ripple components in the output signal of the oxygen concentration
detector 1. The output of the air-fuel ratio discriminating circuit
2, i.e., the output of the comparator 2d is applied to the addition
and subtraction command circuit 3. The addition and subtraction
command circuit 3 comprises a flip-flop 31 and a gating circuit 32.
In operation, a "1" signal appears at the output of one NAND gate
31a of the flip-flop 31 when there is a "1" signal at the output of
the comparator 2d, whereas a "1" signal appears at the output of
the other NAND gate 31b when there is a "0" signal at the output of
the comparator 2d. Numeral 31c designates an inverter for inverting
the output of the comparator 2d and supplying it to the NAND gate
31a. In this way, a different input signal is always applied to the
flip-flop 31 comprising the NAND gates 31a and 31b. The gating
circuit 32 comprises two three-input NAND gates 32a and 32b,
whereby the sampling signals from the sampling signal generating
circuit 4 are added or subtracted depending on the command signal
from the addition and subtraction command circuit 3.
The holding circuit 12 for the reversible counter 5 operates so
that when the count of the reversible counter 5 is held at the
maximum value when the count during the addition exceeds the
maximum counting capacity, whereas the count is held at zero when
the count exceeds the counting capacity during the subtraction,
thereby preventing the application of further sampling signals from
changing the count of the reverisible counter 5 and thus minimizing
the occurrence of errors due to the limitation to the capacity of
the counter 5. A maximum count detecting circuit 101 comparises a
NAND gate 101a, an inverter 101b, a NAND gate 101c with an expander
and a NAND gate 101d and generates pulse signals in such a manner
that the output of the NAND gate 101d has a "0" signal only at the
moment when all the outputs of the reversible counter 5 have a "1"
signal. In other circumstances, a "1" signal appears at the output
of the NAND gate 101d. The NAND gate 101a and the inverter 101b may
be replaced with an AND gate. On the other hand, a zero detecting
circuit 102 comprising four inverters 102a, a NAND gate 102b, an
inverter 102c, a NAND gate 102d with an expander and a NAND gate
102e generates pulse signals in such a manner that a "0" signal
appears at the output of the NAND gate 102e only at the moment when
all the outputs of the reversible counter 5 have a "0" signal.
Otherwise, a "1" signal appears at the output of the NAND gate
102e. A timing pulse generating circuit 103 comprising a NAND gate
103a with an expander and a NAND gate 103b generates timing pulse
signals in such a manner that a "0" signal appears at the output of
the NAND gate 103b at the moment when the output signal of the NAND
gate 31b in the addition and subtraction command circuit 3 changes
from "0" to "1." Otherwise, a "1" signal normally appears at the
output of the NAND gate 103b. In the like manner, a timing pulse
generating circuit 104 comprising a NAND gate 104a with an expander
and a NAND gate 104b generates timing pulse signals so that a " 0"
signal appears at the output of the NAND gate 104b only at the
moment when the signal at the NAND gate 31a changes from "0" to
"1." In other circumstances, a "1" signal normally appears at the
output of the NAND gate 104b. A flip-flop 105 comprising NAND gates
105a and 105b is operated by the command signal or the output of
the addition and subtraction command circuit 3. In other words, in
response to the timing signals from the NAND gates 103b and 104b, a
"1" signal appears at the output of the NAND gate 105a for the
operation of addition, whereas a "1" signal appears at the output
of the NAND gate 105b for the operation of subtraction. When the
count of the reversible counter 5 reaches its maximum counting
capacity so that all the output have a "1" signal, the flip-flop
105 is reset by the NAND gate 101d with the result that the output
of the NAND gate 105a has a "0" signal and the output of the NAND
gate 105b has a "1" signal. The output signal of the NAND gate 105a
is applied to the NAND gate 32a and thus a "1" signal continuously
appears at the output of the NAND gate 32a. Consequently, no
sampling signal is applied to the reversible counter 5 and its
count is maintained at the maximum value. Similarly, in the case of
the subtraction, when all the outputs of the reversible counter 5
have a "0" signal, the flip-flop 105 is reset by the NAND gate 102e
so that a "1" signal appears at the output of the NAND gate 105a
and a "0" signal appears at the output of the NAND gate 105b. The
output signal of the NAND gate 105b is applied to the NAND gate 32b
and thus a "1" signal is continuously produced at the output of the
NAND gate 32b. As a result, no sampling signal is applied to the
reversible counter 5 to maintain its count at zero.
The count of the reversible counter 5 obtained in the
above-described manner is applied to the D-A converter 6 where it
is subjected to digital to analog convertion by means of resistors
6a, 6b, 6c and 6d and a summing amplifier 6e. Therefore, the output
count of the reversible counter 5 is converted to obtain the
stairstep output Vn shown in FIG. 3 which corresponds to the output
count of the reversible counter 5. In this case, the output of the
reversible counter 5 is represented in the 8421 code and thus the
resistors having the corresponding resistance values are provided.
In other words, the resistor 6a having a resistance value R is
connected to the output of the reversible counter 5 representing
the of "8," the weighted resistor 6b having a resistance value 2R
is connected to the output representing "4," the resistor 6c having
a resistance value 4R is connected to the output representing "2"
and the resistor 6d having a resistance value 8R is connected to
the output representing "1." Further, dividing resistors 6f and 6g
are provided so that when the operation of the summing amplifier 6e
is to be started at a potential other than a zero potential, a
suitably divided potential by the dividing resistors 6f and 6g is
applied to the noninverting input of the summing amplifier 6e.
Therefore, if the operation of the summing amplifier 6e needs not
be started at the zero potential (from the standpoint of the
operation of the computing section), the dividing resistors 6f and
6g may be eliminated. A feedback resistor 6h is provided to
maintain the unit voltage .DELTA.v shown in FIG. 3 at a
predetermined value. The output signal of the summing amplifier 6e
is suitably corrected and converted into injection pulses by the
computing unit 7 of the kind used in a known type of electronically
controlled fuel injection system and the injection pulses are used
to actuate the electromagnetic valuve 9 through the electromagnetic
valve actuating circuit 8. The sampling signal generating circuit 4
comprising two NAND gates 4a and 4b generates sampling signals of a
predetermined frequency by suitably selecting capacitances C.sub.1
and C.sub.2 of capacitors 4c and 4d.
Next, the fourth embodiment of the present invention shown in FIG.
9 will be described. The fourth embodiment differs from the first
embodiment of FIG. 1 in that when the response speed of the oxygen
concentration detector 1 decreases, the frequency of the sampling
signals for negative feedback control is decreased to correct the
duration of the energization of the electromagnetic valve 9 and
thereby to control the air-fuel ratio with improved accuracy. For
this purpose, the frequency of the sampling signals from the
sampling signal generating circuit 4 is changed in accordance with
the discrimination output signal from the air-fuel ratio
discriminating circuit 2. This constitutes the only difference of
the fourth embodiment from the first embodiment of FIG. 1. The
response speed of the oxygen concentration detector 1 mounted in
the exhaust pipe 110 of the internal combustion engine 100 has a
gradually falling characteristic as shown by the characteristic
curve A in FIG. 10 when the air-fuel ratio becomes greater than a
predetermined air-fuel ratio so that a transition occurs from the
direction of the signal indicative of "rich" mixture to the
direction of the signal indicative of "lean" mixture, while in the
reverse situation it has an abruptly rising characteristic as shown
by the characteristic curve B in FIG. 10. In other words, it is
believed that the transition from the "rich" mixture state to the
"lean" mixture state is caused by the fact that the deposited fuel
and the like on the wall of the inlet manifold are drawn into the
engine 100 along with the injected fuel.
Accordingly, the output signal of the air-fuel ratio discriminating
circuit 2 is introduced into the sampling signal generating circuit
4 as shown in FIG. 9, whereby when the output signal or
discrimination signal is a "1" signal, the sampling period is
decreased to reduce the frequency of the sampling signals as
compared with the case when the discrimination signal is a "0"
signal. FIG. 11 shows one form of the arrangement for varying the
oscillation frequency of such sampling signal generating circuit 4
comprising a known type of astable multivibrator. The construction
and operation of this sampling signal generating circuit 4 are as
follows. When the discrimination output signal of the air-fuel
ratio discriminating circuit 2 is a "0" signal, it is inverted by
an inverter 41 so that a transistor 40 is turned on and parallel
resistors R are connected to resistors R.sub.1 and R.sub.2 to
increase the oscillation frequency. In other words, the oscillation
period is reduced. In this case, the resistance value of the
resistors R is suitably selected to obtain a proper value for the
oscillation frequency. On the other hand, when the discrimination
output signal of the air-fuel ratio discriminating circuit 2
changes to "1" signal, the transistor 40 turned off to decrease the
oscillation frequency.
FIG. 12 shows another arrangement wherein the sampling signal
generating circuit 4 has a fixed frequency of oscillation, whereby
when the discrimination output signal of the air-fuel ratio
discriminating circuit 2 is a "0" signal, said oscillation
frequency is used as the frequency of the sampling signals, whereas
when the discrimination output signal is a "1" signal, an
oscillation frequency which is 1/n of the fixed oscillation
frequency is used as the oscillation frequency of the sampling
signals. The construction and operation of this sampling signal
generating circuit 4 are as follows. When the discrimination output
signal is a "0" signal, the output signal of an oscillator 411 is
directly supplied through a NAND gate 412 and a NAND gate 416 and
its frequency as such is used as the frequency of the sampling
signals. In this case, the output of a NAND gate 415 always has a
"1" signal.
On the other hand, when the discriminator output signal is a "1"
signal, one input to the NAND gate 412 is applied through an
inverter 417 and thus it is alway a "0" signal causing the NAND
gate 412 to continuously produce a "1" signal. The discrimination
output signal is passed through a NAND gate 413 and it is subjected
to frequency division by a factor of n by a scale-of-n counter 414
from which the signal is passed through the NAND gate 415 and
further through the NAND gate 416. In this way, a frequency which
is one n-th of that of an oscillator 411 is used as the frequency
of the sampling signals. In this case, the NAND gate 415 serves to
maintain a "1" signal at the output of the NAND gate 415
irrespective of the state of the flip-flop at the output stage of
the scale-of-n counter 414 when the discrimination output signal is
passed through the NAND gate 412.
Next, the fifth embodiment of the present invention shown in FIG.
13 will be described. This embodiment differs from the previously
described embodiments in that it further comprises superposing
means whereby an additional correction signal corresponding to the
number of sampling by the sampling signals in the time period up to
the reversal of the polarity of the feedback is superposed on the
negative feedback system provided by the detection of the
concentration of oxygen contained in the exhaust gases. In this
way, where a correction value is used which is varied by a
predetermined amount for each sampling by the sampling signals or
in accordance with the load, such correction value is increased as
a means of eliminating such inconvenience that the occurrence of a
large discrepancy between the reference characteristic and the
desired air-fuel ratio characteristic results in a large time delay
in attaining a predetermined air-fuel ratio or a stable point for
the correction value. Moreover, it is possible to prevent such
inconvenience which may be caused by the limitation to the response
speed of the oxygen concentration detector when the frequency of
sampling signals is increased.
In FIG. 13, numeral 13 designates a superposing D-A converter for
generating an output voltage proportional to the number of sampling
which is dependent on the determination of a level discriminating
circuit 11. Numeral 14 designates an adder for producing the sum of
the output voltage of the D-A converter 6 and the output voltage of
the superposing D-A converter 13, whereby the resultant sum signal
is applied to the computing unit 7 of the kind used in a known type
of electronically controlled fuel injection system for internal
combustion engines and it is used as one of the conventional
correction terms, i.e., as one of the engine parameters to control
the pulse width of the injection pulses produced by the computing
unit 7 and thereby to open the electromagnetic valve 9 connected to
the electromagnetic valve actuating circuit 8 in accordance with
the injection pulses. The level discriminating circuit 11, the
superposing D-A converter 13 and the adder 14 constitute
superposing means 15 whose detailed circuit diagram is illustrated
in FIG. 14. In FIG. 14, the same reference numerals as used in the
first embodiment of FIG. 1 designate the identical or like
component parts.
With the construction described above, the operation of the fifth
embodiment is as follows.
In the same manner as described with reference to the first
embodiment of FIG. 1, the D-A converter 6 generates the required
output signal. On the other hand, the level discriminating circuit
11 determines the number of the sampling signals generated in the
time period up to the reversal of the discrimination output signal
of the air-fuel ratio discrimination circuit 2, i.e., in the time
period during which the discrimination output signal remained at
the same level. In response to the thus determined number of
sampling, the superposing D-A converter 11 produces a superposing
output voltage corresponding to the determined sampling number. To
superpose this superposing output voltage on the output voltage of
the D-A converter 6, the two voltages are added together in the
adder 14. Consequently, the computing unit 7 calculates a pulse
width corresponding to the superposed output voltage of the adder
14 and effects an additive or subtractive correction on the pulse
width of the injection pulses to stabilize it at a value
corresponding to a predetermined air-fuel ratio. In this case, the
addition by the superposing means 15 may include not only simple
additions, but also such additions as including constant multiples
depending on the engine which is to be controlled.
The system according to the fifth embodiment has a remarkable
advantage in that by virtue of the operation of the superposing
means, the stable point can be reached quickly even in a region
where there is a large discrepancy between the fundamental
characteristic of the system installed in the engine and a
predetermined air-fuel ratio characteristic and moreover the range
of the stable region is narrow and the control can be effected with
extremely high accuracy.
Referring now to FIG. 15, a sixth embodiment of the system
according to this invention will be described. The sixth embodiment
differs from the previously described first to fifth embodiments in
that while, in the latter, the D-A converter 6 converts the output
of the reversible counter 5 into a stairstep output voltage as
shown in FIG. 3, a correction value setting circuit 6' of the sixth
embodiment converts the output of the reversible counter 5 into a
stairstep valve energization time or injection time duration as
shown in FIG. 17.
In the sixth embodiment of FIG. 15, the correction value setting
circuit 6' generates correction pulses which correct the injection
time by the rate of unit correction value .DELTA..tau. per each
count in accordance with the output of the reversible counter 5 as
shown in FIG. 17 (if necessary, this correction value may be varied
in accordance with the load of the engine). In this way, the
injection time according to the reference air-fuel ratio
characteristic shown by the solid line in FIG. 18 is varied. The
reference injection time is varied in accordance with the
adjustment of a reference correction value .tau.C and the
electromagnetic valves are opened during the thus modified
injection time. Numeral 7' designates a computing unit by which
injection pulses having a time width corresponding to engine
parameters such as the manifold vacuum and engine temperature are
generated and the correction value setting circuit 6' generates
correction pulses in synchronism with the termination of the
injection pulses to extend the duration of the opening of the
electromagnetic valves by the injection pulses.
With the construction described above, the operation of the sixth
embodiment is as follows. The reference air-fuel ratio
characteristic is predetermined to provide a lean mixture in all
the load ranges and the reference correction value .tau.C which is
a multiple of the unit correction value .DELTA..tau. is added to
ensure a mixture of approximately the predetermined air-fuel ratio.
When the engine is started, the reversible counter 5 is first set
to the maximum count. The reason for setting the reversible counter
5 to the maximum count is that the supply of a relatively rich
mixture is required until the warming up of the engine is over and
thereafter the oxygen concentration detector 1, the air-fuel ratio
discriminating circuit 2 and the addition and subtraction command
circuit 3 cause the reversible counter 5 to count in a direction
which performs the subtraction. Consequently, the correction value
.tau.C is gradually reduced so that if the count corresponding to
the predetermined air-fuel ratio is designated as nx, the
correction value is stabilized within a range on either side of the
count nx (nx .+-. 1). By decreasing the amount of change of the
unit correction value .DELTA..tau. with the air-fuel ratio or
alternately by increasing the capacity of the reversible counter 5,
the stabilization of the correction value with the tolerance of
.+-. 1 count can be made without giving rise to any practical
inconvenience and a highly accurate control can be ensured.
Further, when the operating conditions of the engine change so that
the time width of the correction pulses is to be varied in a
direction which increases the reference correction value .tau.C,
the first sampling causes the oxygen concentration detector 1, the
air-fuel ratio discriminating circuit 2 and the addition and
subtraction command circuit 3 to operate in a dirction which
enriches the air-fuel ratio and consequently the correction pulses
having a time width .tau.C + .DELTA..tau. are supplied from the
correction value setting circuit 6' to the electromagnetic valve 9.
Further, when the air-fuel ratio discriminating circuit 2
determines as the result of the second sampling that the quantity
of fuel is insufficient, the correction value setting circuit 6' is
caused to generate the correction pulses having a time width .tau.C
+ 2.DELTA..tau.. When the further sampling indicates that the
amounts of the previously made corrections are still inadequate,
the correction pulses having a time width .tau.C + 3.DELTA..tau.
are supplied to the electromagnetic valve 9 from the correction
value setting circuit 6' and thus the correction by the air-fuel
ratio feedback is stabilized at the point of .tau.C + n.DELTA..tau.
.+-. .DELTA..tau.. Further change in the operating conditions of
the engine also causes the subtractive operation to take place and
thus the correction value is stabilized at the point of .tau.C -
n.DELTA..tau. .+-. .DELTA..tau..
As described hereinbefore, the result of the determination of the
air-fuel ratio by the preceeding sampling is stored in the
reversible counter 5 so that the addition or subtraction of the
unit correction value .DELTA..tau. is effected depending on the
result of the succeeding sampling and in this way a predetermined
air-fuel ratio can be maintained over the entire operating ranges
of the engine.
FIG. 19 shows a seventh embodiment of the system according to the
present invention. This seventh embodiment differs from the sixth
embodiment of FIG. 15 in that it further comprises a dead zone
detecting circuit 111. In this embodiment, the air-fuel ratio
discriminating circuit 2 compares the output of the oxygen
concentration detector 1 with the setting voltage VR for setting
the air-fuel ratio c and it has a hysteresis characteristic as
shown by the broken line in FIG. 20 depending on whether the
concentration of oxygen contained in the exhaust gases is greater
than or less than the preset oxygen concentration corresponding to
the preset air-fuel ratio to thereby generate a discrimination
output signal which is either a "0" or "1" level. The dead zone
detecting circuit 111 provides a means for detecting the dead zone
and it detects the fact that the output voltage of the oxygen
concentration detector 1 has reached the level of the intermediate
dead zone between the "0" level and the "1" level and prevents the
generation of the sampling signals. FIG. 21 shows a detailed
circuit diagram of the dead zone detecting circuit 111. In FIG. 21,
numeral 111a designates a lower limit comparator for detecting the
lower limit of the intermediate dead zone, 111b an upper limit
comparator for detecting the upper limit of the intermediate dead
zone, 111c an inverter, 111d a NAND gate, 112 a constant pressure
fuel line.
With the construction described above, the operation of the seventh
embodiment is as follows. Assuming now that the air-fuel ratio c is
lower than the value at point c.sub.1 in FIG. 20 and the output of
the air-fuel ratio discriminating circuit 2 is at the "1" level,
the addition and subtraction command circuit 3 generates a command
signal for addition each time the sampling signal is applied to the
addition and subtraction command circuit 3. Consequently, the
reversible counter 5 comes into operation in accordance with the
count stored therein as the result of the preceeding sampling and
the time width of the correction pulses generated by the correction
value setting circuit 6' in accordance with the count of the
reversible counter 5 is increased each time a further sampling is
effected. In this way, the negative feedback control is performed
wherein the duration of the opening of the electromagnetic valve 9
is corrected to increase it by an amount corresponding to the pulse
width of the correction pulses in addition to the duration of the
injection pulses from the computing unit 7' to thereby increase the
air-fuel ratio c.
On the other hand, when the air-fuel ratio c is greater than the
value at point c.sub.4 in FIG. 20 and the output of the air-fuel
ratio discriminating circuit 2 is at the "0" level, the addition
and subtraction command circuit 3 generates a command signal for
subtraction each time it receives the sampling signal and the
reversible counter 5 performs the subtraction operation to decrease
the time width of the correction pulses in accordance with the
count of the reversible counter 5. In this way, the negative
feedback control is effected in which the extension of the duration
of the opening of the electromagnetic valve 9 is decreased to
reduce the air-fuel ratio c. Further, since the output of the
oxygen concentration detector 1 has the output characteristic shown
by the solid line connecting points a.sub.o, a.sub.1, a.sub.3 and
a.sub.5 in FIG. 20, the air-fuel ratio discriminating circuit 2
generates its discrimination output signals of "1" and "0" levels
with the hysteresis characteristic having the loop shown by the
broken line connecting points a.sub.1, a.sub.2, a.sub.3 and a.sub.4
in FIG. 20. Thus, the dead zone detecting circuit 111 is provided
to prevent the occurrence of a phenomenon that the air-fuel ratio c
swings back and force between the points c.sub.1 and c.sub.4 due to
the fact that the fuel quantity is increased or decreased until the
level of the discriminating signal from the air-fuel ratio
discriminating circuit 2 changes. In the dead zone detecting
circuit 111, the lower limit comparator 111a detects a point
b.sub.1 of the characteristic shown in FIG. 20 so that it generates
a detected lower limit signal of "1" level for the air-fuel ratio
on the side of the point c.sub.1 which is smaller than the air-fuel
ratio c.sub.2 corresponding to the point b.sub.1 and the lower
limit signal of "0" level for the air-fuel ratio on the side of the
point c.sub.4 which is greater than the air-fuel ratio c.sub.2. The
output signal of lower limit comparator 111a is inverted by the
inverter 111c and it is then applied to one input of the NAND gate
111d. On the other hand, the upper limit comparator 111b detects a
point b.sub.2 of the characteristic shown in FIG. 20 so that it
generates a detected upper limit signal of "1" level for the
air-fuel ratio on the side of the point c.sub.1 which is smaller
than the air-fuel ratio c.sub.3 corresponding to the point b.sub.2
and the upper limit signal of "0" level for the air-fuel ratio on
the side of the point c.sub.4 which is greater than the air-fuel
ratio c.sub.3. The output of the upper limit comparator 111b is
applied to the other input of the NAND gate 111d. Consequently, the
detected output signal of "0" level is generated only when both of
the inputs to the NAND gate 111d are of the "1" level. In other
words, the detected output signal of the NAND gate 111d becomes a
detected dead zone signal of "0" level when the air-fuel ratio c
reaches and stays within the range of the intermediate dead zone
between the points c.sub.2 and c.sub.3. The dead zone detecting
circuit 111 which generates the above-described detected signal
controls the generation of the sampling signals so that the
generation of the sampling signals is prevented when the air-fuel
ratio reaches and stays between the points c.sub.2 and c.sub.3. As
a result, the addition and subtraction command circuit 3 generates
no command signal and thus the reversible counter 5 performs no
adding or subtracting operation. When this occurs, the correction
value setting circuit 6' generates the correction pulses having the
time width determined by the previous sampling and thereafter the
fuel quantity is increased or decreased with the determined
correction value. Accordingly, when the engine load is constant,
the air-fuel ratio does not swing between the points c.sub.1 and
c.sub.4, but it is controlled to stay at the lower limit point
c.sub.2 or upper limit point c.sub.3 of the intermediate dead
zone.
* * * * *